High-bandwidth, power efficient, and reliable optical links have potential to change the consumer electronics and server markets as Internet data traffic continues to grow exponentially over the years and electronic interconnects are reaching their limits to sustain such growth. Integrated optoelectronic technology can serve as critical enabler to allow personal computing devices to send and receive data at unprecedented rate. In recent years, many successes in optical-component research in the field of silicon photonics have made silicon-on-insulator (SOI) the most promising material-platform-of-choice for the future generations of integrated optoelectronic systems. A typical integrated optoelectronic system could include lasers, modulators, multiplexers/demultiplexers, photo-detectors, and other passive components such as filters and couplers.
Lasers are well known devices that emit light through stimulated emission and produce coherent light beams with a frequency spectrum ranging from infrared to ultraviolet and may be used in a vast array of applications. In an integrated photonic link, data is encoded from a laser source through a modulator and propagates through waveguides. In many applications, the optical data travels through several active and passive components on the same chip, and it is desirable to monitor the optical power at various stages of the system.
Currently, one standard way to monitor optical power inside a waveguide is to collect the light exiting the waveguide with an optical fiber or free-space objective. The optical power may be measured with an external power-meter. The actual power may be determined by assuming some pre-characterized losses, including input/output coupling losses and waveguide propagation loss.
All these loss characterizations are carefully measured and calibrated beforehand. For instance, propagation loss is usually measured via on-chip cutback method, which requires making several bend waveguides with various lengths on the same chip. One would measure the output power from each bended waveguide, and determine the propagation loss via a statistical fit.
The method described above would occupy precious wafer areas, and may only work with simple waveguide structures on a component-level. In an integrated photonic network setting, where many optical components are linked together on the same substrate, the above-mentioned method may not work well. For instance, in the case of a network failure, it is important to find the failing component in the integrated network. Since the above method only determines whether the network is failing, but not where the network is failing, an alternative power monitor scheme is desired.